Supercurrent sign reversal with Aharonov-Bohm interferometry
In collaboration with F. Giazotto from the experimental group at NEST in Pisa, we have investigated the Josephson Effect in a S-N-S junction (S=Superconductor; N=Normal) where the normal region is realized with a ballistic ring.

The underlying idea is that, when the N-region is a quantum interferometer, the supercurrent flowing through the S-electrodes can be manipulated by tuning the parameters of the interferometers.

It has been shown that, by exploiting the electro-magnetostatic Aharonov-Bohm effect in the ring, not only the magnitude but also the sign of the supercurrent can be tuned. The system thus represents a fully tunable pi-junction. The system can be implemented by realizing Aharonov-Bohm rings with semiconductor heterostructures; highly transparent contacts between a semiconductor and superconducting electrodes (such as Niobium and Alluminium) can be obtained with appropriate gradual doping of the former.

Applied techniques
  • Bogolubov-de Gennes Equations
  • Scattering Matrix Theory
  • Analytic Functions Technique

    References
  • F. Dolcini, and F. Giazotto, Switching the sign of Josephson current through Aharonov-Bohm interferometry, Phys. Rev. B 75, 140511 (2007).
  • Carillo et al, Physica E 32, 53 (2006)
  • F.Giazotto et al. APL 78, 1772 (2001)
  • F.Giazotto et al. PRL 87, 216808 (2001)
  • De Franceschi et al. APL 73, 3890 (98)
    		• Fabrizio DolciniFabrizio Dolcini
    Fabrizio Dolcini

    Supercurrent flowing through the device sketched above. By tuning either u (=gate voltage in the lower arm) or Φ (=magnetic flux through the ring), both the magnitude and the sign of the supercurrent can be manipulated.